OCCURRENCE OF OCTADECAPENTAENOIC ACID IN LIPIDS OF A COLD STENOTHERMIC ALGA, PRYMNESIOPHYTE STRAIN B1

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Abstract
The fatty acid composition of the prymnesiophyte strain B, a cold stenothermic microalga, was examined. The major fatty acids derived from the total lipids in this strain were myristic (14:0), palmitic (16:0), oleic (18:1ω9), linoleic (18:2ω6), octadecatetraenoic (18:4ω3), octadecapentaenoic (18:5ω3), and docosahexaenoic (22:6ω3) acids. Octadecapentaenoic acid (18:5ω3) was an unusual component and was characterized by mass spectrometry, infrared absorption spectrometry, and proton nuclear magnetic resonance spectrometry. Saturated fatty acids (14:0 and 16:0) and 18:5ω3 were distributed at significant levels in the major classes of galactolipids (monogalacto‐syldiacylglycerol, digalactosyldiacylglycerol, and sulfoqui‐novosyldiacylglycerol), phospholipids (phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine), and neutral lipids with the exception that phosphatidylethanolamine contained only trace amounts of 14:0. By contrast, 22:6ω3 was distributed in phospholipids and neutral lipids.A decrease in growth temperature from 5°C to 2°C was accompanied by a significant increase in levels of 18: 5ω3 and 18:4ω3 with a concomitant decrease in the level of saturated fatty acids, whereas the level of 22:6ω3 was scarcely changed. These results suggest that, in prymnesiophyte strain B, eighteen‐carbon polyunsaturated fatty acids with more than three double bonds, 18:5ω3 in particular, serve as modulators of membrane fluidity. The potential role of 18:5ω3 as a specific marker for prym‐nesiophytes is also discussed.